Maintaining your Ford Focus' suspension system is important for all driving conditions, especially over rough roads. Proper suspension also offers you a smooth driving experience. Uncomfortable rides over normal roads is an indicator of suspension problems.
Struts are the key components that help prevent the car from wanting to launch off of the road and then slam down during hilly or bumpy drives. As such, feeling your Focus bottoming is an indicator of worn struts. Other signs of worn struts include cupped tires and wheel noise and vibrations while driving.
Ball joints on your Focus connect the wheels to the car's suspension system. They allow the front wheels to move up and down over bumps and side to side when steering. Worn ball joints can cause cupped tires and noise in the front end of the car. A binding in the ball joints can seize the steering wheel from returning to a straight position after a turn.
Your Focus' stabiliser bar prevents excessive body roll when cornering the car and stabilises the car during rough driving conditions. As such, a loose stabiliser bar would cause poor steering stability, excessive rolling when cornering or turning and noise in the front end.